Aircraft manufacturers are continuously seeking ways of increasing aircraft performance and reducing fuel consumption. One of the main factors when it comes to improving aircraft performance, is the aerodynamic drag on aircraft surfaces.
A significant amount of aircraft drag is caused by turbulent air flow on the aircraft exposed surfaces during flight. Near the aircraft skin the air flow is turbulent mainly due to the following reasons:                laminar flow is unstable with respect to small perturbations, and        surface imperfections may cause early transition from laminar to turbulence.        
Since air laminar boundary layers create less friction at the aircraft surfaces than air turbulent boundary layers, one technique for reducing aircraft drag is to form and maintain a laminar boundary layer over the aircraft external surfaces.
Laminar Flow reduces friction drag and implementation on vertical tail planes (VTP) and horizontal tail planes (HTP), would potentially lead to up to 2% aircraft drag reduction.
Current existing methods to form and maintain a laminar flow are:                Natural Laminar Flow (NLF) is obtained by a profile that produces a progressive pressure drop (i. e. favourable gradient) resulting in flow acceleration and a delay in transition to turbulence approximately at the point of minimum pressure.        Laminar Flow Control (LFC) which relies on a relatively small amount of air being sucked through a perforated skin to suppress boundary layer instabilities.        Hybrid Laminar Flow Control (HLFC) is a combination of full LFC and NLF as shown in FIG. 1, which relies on:        
1. suction being applied to the leading edge (1) 10-20% of the chord (i. e. ahead of the front spar), to stabilize the flow, and
2. a correctly profiled wing or lifting surface contour, to generate a suitable pressure gradient, thus maintaining the laminar flow aft of the suction area.
Transition from laminar to turbulent flow, is delayed by this technique, and may even occur after the 50% chord location, due to the combined effects of the local pressure gradient and Reynolds number.
FIG. 2 shows a laminar flow control system, to actuate on the boundary layer by bleeding air through a micro-perforated skin surface (3) at the leading edge (1). Typically, the diameter of the micro-perforations is within the range 10-100 microns. The air is ducted beneath the skin (3) through a network of chambers (2) located at the leading edge section (D-box) (1), and finally exhausted, through a main chamber or a suction duct (4).
As suction is limited to the forward part of the wing or lifting surface, HLFC avoids many of the structural problems associated with LFC. It also requires a smaller and lighter suction system. These advantages make HLFC more suitable than full LFC for subsonic transport aircraft. The HLFC technology has also good aerodynamic performance in the fully turbulent mode, which is a significant advantage.
This air suction system of the leading edge (1) requires a differential pressure distribution over the leading edge surface. This differential pressure distribution is achieved by providing chambers of different size, to obtain different pressure within each chamber, as shown more clearly in FIG. 2C.
As shown in FIG. 3, a conventional leading edge configuration with laminar flow control, is formed by a micro-perforated outer skin (3), a perforated inner skin (5) and a set of transversal walls (6) fixed to outer and inner skins at specific locations to form chambers of different sizes, to create the chambers allowing air circulation through them.
One of the main problems involved in the implementation of the HLFC technique, is that the components of the leading edge have to be manufactured separately and then assembled together. In addition to this, assembly by means of mechanical joints may reduce the effective outer suction surface. Thus, manufacturing and assembly processes of these multi-chambered structures with laminar flow control, are complicated and expensive. Furthermore, the weight penalty involved is significantly high due to the metallic materials implemented and the length of all mechanical joints used for building the leading edge, penalizing so much the aircraft performances that all HLFC benefits would be overcame and, as consequence, its implementation may be discarded.